1. Field of the Invention
This invention relates to an improved process for the preparation of hot water from solar energy.
2. Description of the Prior Art
Among the processes for the preparation of hot water from solar energy which have already been described, the one forming the subject of U.S. Pat. No. 4,165,732 is known in particular. That patent describes a process for heating water with storage means comprising two storage tanks, one of which is heated by solar energy and the other by non-solar energy. The description specifies that the heat-carrying fluid used can be water with a glycol additive to eliminate the risks of freezing. Unfortunately, health and safety regulations tend to forbid the use of various commercial antifreeze products such as the glycols owing to the risks of these products mixing with the sanitary water in the event of leakages from the exchanger. The possible use of anhydrous heat-carrying fluids such as the terphenyls also poses problems in the event of leakage and mixing with the sanitary water. In addition the heat transfer properties of these fluids are well below those of water and their viscosity is higher. Obviously, whatever precautions are taken, it is impossible to guarantee that a heat exchanger device be sealed under all circumstances over a period of ten years or more. The possible use of double-walled tubes to produce the exchanger, with an intermediate layer of pure water is an expensive solution which is difficult to bring into practical use.
For all these reasons, the possibility has been investigated of using pure water even in regions where the temperature of the solar collector can fall below 0.degree. C. at night during certain periods of the year. In order to be able to use ordinary water in this way, the present invention generally provides for automating the operations of draining and filling of the solar collector each time that its temperature drops below 0.degree. C. then rises above this temperature again at the end of an undetermined period.